The Wagners allege they were accused of the deaths of 12 people in the town of Grantham during the 2011 floods, when one of the walls of the Lockyer Valley quarry they owned collapsed.

The Toowoomba-based brothers claim they were also subjected to constant abuse, including accusations of a high-level cover-up with politicians, corruption and intimidation relating to their Wellcamp Airport.

Most of Jones' remarks were made on radio stations 2GB and 4BC, while one was made on his Sky News television program.

If the lawsuit is successful, Jones and his co-accused could be liable for $4.8 million in damages.

On the opening day of the Brisbane Supreme Court trial this month, the Wagner brothers' barrister Tom Blackburn QC said it was a landmark case.

"It's the sheer volume of these charges and the relentlessness of them your honour that sets this case apart," he said.

"If the statements were not lawfully excusable in some way then the damages, in our submission, must be very large indeed because as we say they constitute a defamation that is unparalleled as far as we're aware in this country."

The court has heard Jones, his employers and Cater intend to rely on honest opinion as a defence.

Jones, who watched on from the gallery during the opening week of the trial, is set to start giving evidence on Thursday.